1. Field of the Invention
This invention relates to an apparatus for determining the permeability of a web to air, comprising a testing head, which is adapted to be airtightly applied to the web and operable to suck or blow a stream of measuring air through the web, and a connecting line for a device for measuring the stream of measuring air.
2. Description of the Prior Art
For the determination of the permeability of sieves, woven fabrics or felts to air it is known to provide a testing head, which is applied to the web to be tested and is used to suck a stream of measuring air through the web under a predetermined suction pressure in a predetermined suction area and to measure said stream of air. For that purpose the testing head which defines the predetermined suction area must airtightly be applied to the web so that a suction of inleaked air will be prevented, which would adversely affect the result of the measurement. For that purpose the conventional testing heads have an annular seal, which defines the suction area and consists of rubber-elastic, soft material. Such seals have proved satisfactory with testing heads which do not move relative to the web. But difficulties will arise if such seal is used in a testing head which is moved relative to the web because a rapid wear is to be expected so that the required airtight joint between the suction opening of the testing head and the web can no longer be ensured. But for a continual inspection of webs for their permeability to air it would be desirable to provide a testing head which permits of a continuous movement of the web past the testing head.